Electrophotographic imaging members, e.g., photoreceptors, typically include a photoconductive layer formed on an electrically conductive substrate. The photoconductive layer is an insulator in the substantial absence of light so that electric charges are retained on its surface. Upon exposure to light, charge is generated by the photoactive pigment, and under applied field charge moves through the photoreceptor and the charge is dissipated.
In electrophotography, also known as xerography, electrophotographic imaging or electrostatographic imaging, the surface of an electrophotographic plate, drum, belt or the like (imaging member or photoreceptor) containing a photoconductive insulating layer on a conductive layer is first uniformly electrostatically charged. The imaging member is then exposed to a pattern of activating electromagnetic radiation, such as light. Charge generated by the photoactive pigment move under the force of the applied field. The movement of the charge through the photoreceptor selectively dissipates the charge on the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image. This electrostatic latent image may then be developed to form a visible image by depositing oppositely charged particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the imaging member directly or indirectly (such as by a transfer or other member) to a print substrate, such as transparency or paper. The imaging process may be repeated many times with reusable imaging members.
An electrophotographic imaging member may be provided in a number of forms. For example, the imaging member may be a homogeneous layer of a single material such as vitreous selenium or it may be a composite layer containing a photoconductor and another material. In addition, the imaging member may be layered. These layers can be in any order, and sometimes can be combined in a single or mixed layer.
Typical multilayered photoreceptors have at least two layers, and may include a substrate, a conductive layer, an optional charge blocking layer, an optional adhesive layer, a photogenerating layer (sometimes referred to as, and used herein interchangeably, a “charge generation layer,” “charge generating layer,” or “charge generator layer”), a charge transport layer, an optional overcoating layer and, in some belt embodiments, an anticurl backing layer. In the multilayer configuration, the active layers of the photoreceptor are the charge generating layer (CGL) and the charge transport layer (CTL).
As more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, however, degradation of image quality was encountered during extended cycling. The complex, highly sophisticated duplicating and printing systems operating at very high speeds have placed stringent requirements, including narrow operating limits, on the imaging members. Thus, photoreceptor materials are required to exhibit, not only efficient charge generation and charge transport properties, but also structural integrity and robustness so as to withstand mechanical abrasion during image development cycles.
Organic photosensitive pigments are widely used as photoactive components in charge generating layers. One such pigment used in the CGL in electrophotographic devices is titanyl phthalocyanines (TiOPc). As explained in U.S. Pat. No. 5,164,493, which is hereby incorporated by reference in its entirety, polymorphism or the ability to form distinct solid state forms is well known in phthalocyanines. For example, there are four main crystal forms of TiOPc known, Types I, II, III and IV. TiOPc Type IV offers many attractive features as a photosensitive pigment, but is especially of interest because of its high efficiency of charge generation. For example, TiOPc Type IV is a faster photosensitive pigment than hydroxygallium phthalocyanine (HOGaPc). The Type IV polymorph is made by a polymorphic conversion from the Type I polymorph, as disclosed, for example, in U.S. Pat. No. 5,189,155, which is hereby incorporated by reference in its entirety. General processes for making the Type I polymorph are disclosed in U.S. Pat. Nos. 4,664,997, 4,728,592, 4,898,799, 5,132,197, 5,189,155, 5,189,156 and H1,474, which are hereby incorporated by reference in their entirety. Many conventional processes for making TiOPc Type I use 1-1-chloronaphthalene as a reaction solvent. Because 1-chloronaphthalene is a chlorinated solvent, the processes using 1-chloronaphthalene produce chlorinated waste. Such chlorinated waste is toxic and thus presents difficulties in disposal. In fact, 1-chloronaphthalene itself is toxic and presents safety handling issues. Due to these serious toxicity and safety issues associated with. 1-chloronaphthalene, it is no longer commercially available in North America. Thus, there is a need for a new solvent that has the desirable properties of 1-chloronaphthalene, such as a being chemically inert, and having a high boiling point, but without the toxicity. Most importantly the solvent has to be selective to produce TiOPc Type I in the synthesis and the TiOPc type I thus produced should convert to the high photosensitivity TiOPc Type IV crystal form with the desired photoactive properties. In addition, the solvent needs to be commercially available and economical.